The present invention relates to filters generally, and is more specifically directed to a filter which is particularly suited for use in air handling systems which handle large volumes of air, wherein long service live and "blow out resistance" is necessary.
Filters and filter media are used in many applications for filtering gases and liquids. The use of filters, for filtering gases, particularly air in air handling systems, is well known. Such filters as are commonly used in air handling systems are characterized by a frame, in which a filter media is present within the perimeter of the frame. A rigid backing maybe placed within the frame downstream of the filter media to aid in retaining the filter media within the frame, while allowing air to pass through the filter.
In certain applications, such as air handling systems where high volumes of air are circulated through the system, "blow out" is encountered. "Blow out" may be defined as separation of the filter media from the frame, typically at the point of bonding of the media to the frame. Pressure on the media which exceeds the strength of the bonding means will result in such blow out.
Such blow outs may have seriously adverse consequences. Blow outs allow carbon, dust, or other material previously trapped to enter into the system, where it may cause damage to the mechanism which the filter protects. The filter media itself, as it is separated from the frame, will also enter the system, causing damage to the system, or resulting in harmful localized atmospheric conditions, especially in a closed recirculating system. Blow outs may go undetected for some period of time, and filters may be located in areas which make frequent servicing difficult.
In high volume applications, the filter media maybe pleated. This pleating increases the effective filter surface area. Frequently, before blow out, these pleats will collapse, increasing the differential pressure across the filter. Points of high pressure on the upstream side which result from the collapsing pleats increase the likelihood of filter blow out.
The present invention uses a frame and filter media. The present invention prevents blow outs by using a rigid, porous backing which is congruent with the shape of the filter media so as to contact the media at all points and provide support to prevent blow out. The backing may further encapsulate one or more edges of the filter media on the upstream side to aid in shape retention of the media, and further aid in holding the media in place to deter media blow out.